1. Field of the Invention
The present invention relates to a torque fluctuation absorbing device for an engine which is attached to, for example, an engine mounted on a car, for absorbing torque fluctuations of a crank shaft.
2. Description of the Related Art
It is well known that, at a crank shaft of a four-cycle engine mounted on a car, considerably large torque fluctuations can occur at low-speed rotation such as the idling state, which may cause unpleasant vibrations in a car body and impair riding comfort. When, for example, the idling speed of an engine is lowered with the purpose of improving fuel cost performance, it is difficult to fully prevent rolling vibrations caused by torque fluctuations in a conventional engine.
As one of the measures against this problem, there is considered a method that a moment of force is generated between an engine block and a crank shaft by an electromagnetic action, but such a mechanism causes other problems that extremely complicate the structure of the engine and its weight is remarkably increased, therefore, the method has not been put to practical use yet.
Also, in Japanese Examined U.M. Publication No. 2-32890, a device is disclosed in which an additional mass body is provided inside a clutch in addition to a main flywheel and the mass body is engaged with a crank shaft of an engine by an auxiliary clutch interlocking with a main clutch, but with a torque fluctuation absorbing device for an engine using inertial force of the mass body, it is difficult to fully absorb large torque fluctuations at idling speed unless a flywheel with an extremely large inertial moment is used.
Moreover, in another conventional example, one or several balance shafts with an unbalanced weight attached are provided in parallel with a crank shaft, but the physical size and the structure of the engine must be increased and becomes extremely complicated, and a vibration isolation effect is not gained depending on the engine speed.